The present invention relates to a line filter used for a variety of consumer products, and the like.
A conventional line filter will be described hereinafter with reference to the accompanying figures.
In FIG. 55 and FIG. 56, the conventional line filter is provided with bobbin 32 having a through hole, first coil 33 and second coil 34 wound on the bobbin 32, and closed-loop magnetic core 35 inserted in the through hole of the bobbin 32.
They thus constitute noise suppression means to eliminate common mode noises, as shown in FIG. 57 and FIG. 58. This noise suppression means eliminates noises by making magnetic flux A and magnetic flux B generated respectively by the first coil 33 and the second coil 34 flow into the closed-loop magnetic core 35 equally in the same direction, in a manner not to cancel with each other.
When common mode noise 36 propagates into an electric circuit, as shown in FIG. 57, the magnetic flux A and the magnetic flux B generated in the line filter are in directions shown in FIG. 58, due to the above-described structure.
That is, in FIG. 58, the magnetic flux A generated by the first coil 33 and the magnetic flux B generated by the second coil 34 are in the same direction equally, and flow in the closed-loop magnetic core 35 in a manner that they are combined together instead of being cancelled.
A frequency-attenuation characteristic in this instance is given as shown in FIG. 59.
High frequency noise currents generated in an electric circuit through commercial power supply generally include in-phase current and differential current, and the former is called common mode noise and the latter is called normal mode noise.
Although the above-described structure of the prior art can eliminate common mode noise 36, a frequency band in which the common mode noise 36 can be eliminated in this case is usually in the region of low frequency band, as shown in FIG. 59. It therefore has a problem of poor elimination characteristic for the common mode noise 36, as it is unable to attenuate over a wide frequency and from low frequency region to high frequency region.
The present invention addresses the above-described problem, and it is intended to provide a line filter having an outstanding attenuation characteristic over a wide frequency band from low frequency region to high frequency region, with an improved elimination characteristic for the common mode noise.
To achieve the above object, the present invention incorporates a first bobbin and a second bobbin, each of which has a through hole in an axial direction and a winding slot where a coil is wound, a first coil wound around the winding slot of the first bobbin to form a first coil unit, a second coil wound around the winding slot of the second bobbin to form a second coil unit, a closed-loop magnetic core having a magnetic frame-bar inserted in the through holes of the first bobbin and the second bobbin, and a first noise suppression means for eliminating common mode noise.
The first noise suppression means comprises a first noise suppressor for first band to eliminate common mode noise in a first frequency band and another first noise suppressor for second band to eliminate common mode noise in a second frequency band.
The first noise suppressor for first band eliminates noises with the first coil and the second coil so wound that magnetic flux generated by the first coil and another magnetic flux generated by the second coil enhance each other in the closed-loop magnetic core.
The first noise suppressor for second band has a spirally wound first coil for second band, which forms a first coil unit for second band, and a spirally wound second coil for second band, which forms a second coil unit for second band. The first coil for second band and the second coil for second band are so wound that magnetic flux generated by the first coil unit for second band and magnetic flux generated by the second coil unit for second band enhance each other. Noises are eliminated by such an arrangement of the first coil unit for second band and the second coil unit for second band that they are orthogonal to the closed-loop magnetic core, so that a direction of magnetic fluxes generated by the first coil unit and the second coil unit and a direction of magnetic fluxes generated by the first coil unit for second band and the second coil unit for second band cross orthogonally with respect to each other.
In the foregoing structure, the first coil for second band and the second coil for second band are wound in a manner that the magnetic flux generated by the first coil unit for second band and the magnetic flux generated by the second coil unit for second band enhance each other, to eliminate the common mode noise in the second frequency band. It is therefore easy to set a frequency band that can be attenuated by the first coil unit for second band and the second coil unit for second band in a region outside of a frequency band that can be attenuated by the first coil unit and the second coil unit. In addition, it realizes attenuation widely from low frequency region to high frequency region, thereby improving the attenuation characteristic.
In this instance, in particular, the first coil unit for second band and the second coil unit for second band are arranged orthogonal to the closed-loop magnetic core, so that a direction of the magnetic fluxes generated by the first coil unit and the second coil unit and a direction of the magnetic fluxes generated by the first coil unit for second band and the second coil unit for second band cross orthogonally with respect to each other. For this reason, the magnetic fluxes generated by the first coil unit and the second coil unit do not influence with the magnetic fluxes generated by the first coil unit for second band and the second coil unit for second band. This prevents attenuation characteristic of the second frequency band from causing an adverse effect to attenuation characteristic of the first frequency band. Furthermore, the attenuation characteristics can be improved since the attenuation characteristics covering a frequency band is positively broadened.